Device and method for brazing a heat pipe

ABSTRACT

The present invention relates to a device and method for brazing a heat pipe assembly with copper-silver alloy filler rings to improve heat dissipation efficiency of a heat pipe. The device comprises a brazing furnace and a conveyor. The brazing furnace comprises an open ended passage with a multi-stage brazing heater and cooler. The conveyor comprises an input bracket assembly, an output bracket assembly and a steel mesh belt. The method comprises steps of (A) providing multiple heat pipe components, (B) assembling the heat pipe components to form heat pipe assemblies, (C) injecting mixed gas, (D) turning on the multi-stage brazing heater and cooler, (E) placing the heat pipe assemblies on the conveyor, (F) brazing the heat pipe assemblies to form heat pipes, (G) cooling the heat pipes and (H) removing the heat pipes from the conveyor.

FIELD OF THE INVENTION

The invention relates to a device and method for brazing a heat pipewith copper-silver alloy filler to improve heat dissipation efficiencyof the heat pipe.

BACKGROUND OF THE INVENTION

With recent reductions in electronic equipment size) performance ofelectronic equipment has increased dramatically. Higher performance hasresulted in more internal heat and higher operating temperature. Withouteffective dissipation of the internal heat, reliability and life span ofthe associated electronic equipment is adversely affected.

To dissipate heat from electronic equipment, conventional heat sinks andfans are used. Since heat is dissipated at a heat transfer rateproportional to a conventional heat sink's surface area, fins areattached to the heat sink to increase the surface area so more heat willbe dissipated. However, small, modern electronic equipment size limitshow many and how large fins can be, which provides an upper limit to howmuch heat can be effectively dissipated by a heat sink attached to theelectronic equipment. Since heat pipes transfer heat at a much higherrate than heat sinks and fans and can be made to be much smaller than aheat sink and fan, heat pipes are excellent candidates for heatdissipation in small, high performance electronic equipment.

$\frac{\mathbb{d}Q}{\mathbb{d}t} = {h \cdot {A\left( {T_{0} - T_{env}} \right)}}$

Where

-   -   Q=Thermal energy in Joules    -   h=Heat transfer coefficient    -   A=Surface area of the heat being transferred    -   T₀=Temperature of the object's surface    -   T_(env)=Temperature of the environment

Specifically, the heat transfer coefficient (h_(wf)) of a working fluidin a heat pipe is much higher than the heat transfer coefficient (h_(a))of air as in a heat sink or fan.

In a conventional assembly process of a heat pipe, tin is often used asa filler to braze components of the heat pipe together and is coveredwith flux to reduce oxidation of the tin. However, tin has a low meltingpoint and heat-transfer coefficient (h) and is poorly suited todissipate heat generated by high performance electronic equipment. Inaddition, traditional heat pipe components soldering with tin can notpass a reduction procedure at 400° C. Therefore, reliability of the heatpipe is poor.

The heat pipe is hollow and air-tight, has an internal cavity, an insidesurface and a wick and has a vacuum inside to maintain its heat-transferefficiency. However, flux covering the components of heat pipe maydegrade performance of the wick on the inside surface inside the heatpipe and decrease the heat-transfer efficiency of the heat pipe byraising the evaporation and condensation temperatures of the workingfluid.

In a conventional heat pipe manufacturing process, the heat pipe isusually between 100 millimeter and 300 millimeter in length, is cut tofit a product specification and sealed at one end. The sealed end cannottransfer heat. The bigger the heat pipe is, the longer the sealed endis. Therefore the sealed end reduces the heat-transfer efficiency of theheat pipe.

SUMMARY OF THE INVENTION

The objective of the present invention is to braze a heat pipe with acopper-silver alloy filler to improve heat dissipation efficiency of theheat pipe.

A device for brazing a heat pipe comprises a brazing furnace and aconveyor. The brazing furnace comprises an open ended passage with amulti-stage brazing heater and cooler. The conveyor comprises an inputbracket assembly, an output bracket assembly and a steel mesh belt.

A method for brazing a heat pipe in accordance with the presentinvention comprises steps of (A) providing multiple heat pipecomponents, (B) assembling the heat pipe components, (C) injecting mixedgas, (D) turning on the multi-stage brazing heater and cooler, (E)placing the heat pipe assemblies on the conveyor, (F) brazing the heatpipe assemblies, (G) cooling the heat pipes and (H) removing the heatpipes from the conveyor.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a device in accordance with the presentinvention for brazing components of a heat pipe.

FIG. 2 is a flow chart of a method in accordance with the presentinvention for brazing components of a heat pipe.

FIG. 3 is an exploded perspective view of primary components of a heatpipe to be brazed with the method in FIG. 2.

FIG. 4 is a partially exploded perspective view of components of a heatpipe to be brazed with the method in FIG. 2.

FIG. 5 is a perspective view of assembled components of a heat pipe tobe brazed with the method in FIG. 2.

FIG. 6 is a perspective view of components of a heat pipe brazed withthe method in FIG. 2.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

With reference to FIGS. 1, 3, 4, 5 and 6, a device in accordance withthe present invention brazes components of a heat pipe (2) having a pipe(21), a base (22), a cover (23), a small pipe (24) and multiplecopper-silver alloy fillers (25A, 25B, 26) using a method in accordancewith the present invention to braze the components. The pipe (21) ishollow and has a diameter, a lower end, an upper end, an inside surfaceand a wick. The base (22) is larger than the diameter of the pipe (21),has an upper surface and is mounted on the lower end of the pipe (21).The upper surface of the base (22) has an optional recess in which thelower end of the pipe may be mounted. The cover (23) is mounted in theupper end of the pipe (21) and has a central through-hole (231). Thesmall pipe (24) is mounted in and protrudes longitudinally from thecentral through-hole (231). The copper-silver alloy filler rings (25A,25B, 26) comprise two large filler rings (25A, 25B) and a small fillerring (26). The large filler rings (25A, 25B) correspond to the pipe (21)and comprise a large upper filler ring (25B) and a large lower fillerring (25A). The large upper filler ring (25B) is mounted on the upperend of the pipe (21) against the cover (23). The large lower filler ring(25A) is mounted around the pipe (21) and against the base (22). Thesmall filler ring (26) corresponds to the small pipe (24) and is mountedaround the small pipe (24) and against the cover (23).

The device for brazing components of a heat pipe (2) with thecopper-silver alloy fillers (25A, 25B, 26) to improve heat dissipationefficiency of the heat pipe (2) comprises a brazing furnace (11) and aconveyor (12).

The brazing furnace (11) is an elongated structure, has an input end andan output end and comprises a housing (111), a steel liner (112),multiple injection nozzles, a multi-stage brazing heater and a cooler.

The housing (111) is made of fire brick and has an input end, an outputend, an internal, longitudinal passage, multiple mixed gas injectionports (1111), a cooling medium input (112) and a cooling mediumdischarge (1113). The input end has an opening. The output end has anopening that corresponds to and is aligned with the opening in the inputend. The internal, longitudinal passage is formed between andcommunicates with the openings in the input and output ends and isstraight. The mixed gas injection ports (1111) are formed at intervalsalong the housing (111). The cooling medium input (1112) is formedthrough the housing (111) near the output end. The cooling mediumdischarge (1113) is formed through the housing (111) near the outputend.

The steel liner (112) corresponds to and is mounted in the internal,longitudinal passage and comprises an inner wall, a smooth floor andmultiple temperature sensors (1121). The inner wall has multiple mixedgas through-holes (1122), two cooling medium through-holes (1123),opposite sides and a ceiling. The mixed gas through-holes (1122)correspond to and align respectively with the mixed gas injection ports(1111) in the housing (111). The cooling medium through-holes (1123)correspond to and align respectively with the cooling medium input(1112) and discharge (1113). The temperature sensors (1121) are mountedlongitudinally at intervals on the inner wall of the steel liner (112).

The injection nozzles are mounted detachably respectively in alignedpairs of mixed gas injection ports (1111) in the housing (111) and mixedgas through-holes (1122) in the steel liner (112) and connect to anexternal mixed gas source.

The multi-stage brazing heater is mounted in the steel liner (112) ofthe brazing furnace (11) adjacent to the input end and comprises atleast two heating elements (114). Each heating element (114) is formedin a wave shape and is mounted on the sides and ceiling of the innerwall of the steel liner (112). Adjacent heating elements (114) maylongitudinally overlap somewhat.

The cooler is mounted in the steel liner (112) of the brazing furnace(11) between the multi-stage brazing heater and the opening in theoutput end and comprises at least one cooling element (115) and at leastone cooling medium input nozzle and one cooling medium discharge nozzle.The cooling element (115) is mounted on the inner wall and connects tothe cooling medium through-holes (1123).

The conveyor (12) moves assembled components of heat pipes (2) throughthe brazing furnace (11) to melt the copper-silver alloy filler rings(25A, 25B, 26) to securely join components of a heat pipe (2) and fillany gaps between components and comprises an input bracket assembly(121), an output bracket assembly (122) and a steel mesh belt (123).

The input bracket assembly (121) is mounted adjacent to the input end ofthe brazing furnace (11) and comprises a flat top, two elongated legsand a drive pulley. The flat top is parallel to the floor of the steelliner (112) and has a front edge, two side edges and a rear edge. Thefront edge may abut the input end of the housing (111). The rear edgehas a rectangular notch. The elongated legs are connected respectivelyto the side edges of the flat top and protrude down. The drive pulley isrotatably mounted between the elongated legs under the flat top, isaligned with the rectangular notch in the rear edge and may be driven bya motor mounted under the flat top by a shaft or gear train.

The output bracket assembly (122) is mounted adjacent to the output endof the brazing furnace (11) and comprises a flat top, two elongated legsand an idler. The flat top is parallel to the floor of the steel liner(112) and has a rear edge, two side edges and a front edge. The rearedge may abut the output end of the housing (111). The front edge has arectangular notch. The elongated legs are connected respectively to theside edges of the flat top and protrude down. The idler is rotatablymounted between the elongated legs under the flat top and is alignedwith the rectangular notch in the front edge.

The steel mesh belt (123) is mounted around the drive pulley of theinput bracket assembly (121) and the idler of the output bracketassembly (122) in a loop and comprises an upper outbound leg and a lowerreturn leg.

The upper outbound leg after passing around the drive pulley slidesalong the flat top of the input bracket assembly (121) on which heatpipe assemblies (2′) that have not been brazed are placed on the steelmesh belt (123), the floor of the steel liner (112) of the brazingfurnace (11) and the flat top of the output bracket assembly (122) andextends around the idler. The lower return leg extends from the idler,passes under the output bracket assembly (122), the brazing furnace (11)and the input bracket assembly (121) and engages the drive pulley.

With further reference to FIG. 2, the method for brazing components of aheat pipe (2) having a pipe (21), a base (22), a cover (23), a smallpipe (24) and multiple copper-silver alloy fillers (25A, 25B, 26)comprises steps of (A) providing multiple heat pipe (2) components, (B)assembling the heat pipe (2) components, (C) injecting mixed gas, (D)turning on the multi-stage brazing heater and cooler, (E) placing heatpipe assemblies (2′) on the conveyor (12), (F) brazing the heat pipeassemblies (2′), (G) cooling the beat pipes (2) and (H) removing theheat pipes (2) from the conveyor (12).

The step of (A) providing multiple beat pipe components comprisesobtaining heat pipe (2) components comprising pipes (21), bases (22),covers (23), small pipes (24) and copper-silver alloy filler rings (25A,25B, 26). The pipes (21) are hollow, and each pipe (21) has a lower endand an upper end. Each base (22) is larger than the pipe (21) and has anupper surface and an optional recess. The recess corresponds to the pipe(21). Each cover (23) includes a central through-hole (231). The smallpipes (24) correspond respectively to the central through-holes (231).

The step of (B) assembling the heat pipe components to form heat pipeassemblies (2′) comprises steps of (B1) assembling primary components ofthe heat pipe (2) and (B2) mounting copper-silver alloy filler rings(25A, 25B, 26) respectively at joints between primary components.

The step of (B1) assembling primary components of the heat pipe (2)comprises mounting the lower end of the pipe (21) on the upper surfaceof the base (22), mounting the cover (23) on the upper end of the pipe(21) and mounting the small pipe (24) in the central through-hole (231).However, gaps will exist between primary components after this assemblystep.

The step of (B2) mounting the copper-silver alloy filler rings (25A,25B, 26) respectively at joints between the primary components willcause the copper-silver alloy filler rings (25A, 25B, 26) to fill andclose gaps between primary components when brazed and melted.

The step of (C) injecting mixed gas comprises injecting N₂, NH₄ and H₂in a ratio of 2:1:1 into the steel liner (112) of the brazing furnace(11) at the heating elements (114).

The step of (D) turning on the multi-stage brazing heater and coolercauses the initial stage to heat to approximately 220° C. and burn themixed gas to evacuate most oxygen in the brazing furnace (11) and removeany impurities from inside the steel liner (112) to obviate oxidation ofthe heat pipe assemblies (2′) in the brazing furnace (11).

The step of (E) placing the heat pipe assemblies (2′) on the conveyor(12) comprises placing the heat pipe assemblies (2′) on the conveyor(12) sliding on the input bracket assembly (121) to be carried into andthrough the brazing furnace (111).

The step of (F) brazing the heat pipe assemblies (2′) to form heat pipes(2) comprises moving the heat pipe assemblies (2′) through themulti-stage heating elements (114), heating the heat pipe assemblies(2′) to approximately 780° C. and melting the copper-silver alloy fillerrings (25A, 25B, 26) to fill any gaps.

The step of (G) cooling the heat pipe (2) comprises moving the brazedheat pipes (2) through the cooling element (15) and onto the outputbracket assembly (122) after the heat pipes (2) are cooled toapproximately 150° C.

The step of (H) removing the heat pipe (2) from the conveyor (12)comprises removing the heat pipes (2) from the output bracket assembly(122) after the molten copper-silver alloy filler rings (25A, 25B, 26)solidify may be performed robotically.

The heat pipes (2) manufactured by the device and method in accordancewith the present invention can pass a reduction procedure at 400° C., athermal shock testing between −80° C. and 150° C. and a high temperaturetesting at 300° C. for 72 hours to have good reliability, can maintainits heat conductivity during normal operation and can be used in a fieldof IC design, LED module and thermal energy recycling. The field ofthermal energy recycling includes waste heat, hot water, solar energyindustry and so like.

1. A device for brazing components of a heat pipe having a pipe beinghollow and having a diameter, a lower end, an upper end, an insidesurface and a wick; a base being larger than the diameter of the pipe,having an upper surface and being mounted on the lower end of the pipe;a cover being mounted in the upper end of the pipe and having a centralthrough-hole; a small pipe being mounted in and protrudinglongitudinally from the central through-hole; and multiple copper-silveralloy filler rings being a large upper filler ring being mounted on theupper end of the pipe against the cover, a large lower filler ring beingmounted around the pipe and against the base and a small filler ringcorresponding to the small pipe and being mounted around the small pipeand against the cover, the device comprising a brazing furnace being anelongated structure, having an input end and an output end andcomprising a housing being made of fire brick and having an input endhaving an opening; an output end having an opening corresponding to andbeing aligned with the opening in the input end; an internal,longitudinal passage being formed between and communicating with theopenings in the input and output ends and being straight; multiple mixedgas injection ports being formed at intervals along the housing; acooling medium input being formed through the housing near the outputend; and a cooling medium discharge is formed through the housing nearthe output end; a steel liner corresponding to and being mounted in theinternal, longitudinal passage and comprising an inner wall havingmultiple mixed gas through-holes corresponding to and aligningrespectively with the mixed gas injection ports in the housing; twocooling medium through-holes corresponding to and aligning respectivelywith the cooling medium input and discharge; opposite sides; and aceiling; a smooth floor; and multiple temperature sensors being mountedlongitudinally at intervals on the inner wall of the steel liner;multiple injection nozzles being mounted detachably respectively inaligned pairs of mixed gas injection ports in the housing and mixed gasthrough-holes in the steel liner and connecting to an external mixed gassource; a multi-stage brazing heater being mounted in the steel liner ofthe brazing furnace adjacent to the input end and comprising at leasttwo heating elements with each heating element being formed in a waveshape and being mounted on the sides and ceiling of the inner wall ofthe steel liner; and a cooler being mounted in the steel liner of thebrazing furnace between the multi-stage brazing heater and the openingin the output end and comprises at least one cooling element beingmounted on the inner wall and connecting to the cooling mediumthrough-holes; at least one cooling medium input nozzle; and at leastone cooling medium discharge nozzle; and a conveyor moving assembledcomponents of heat pipes through the brazing furnace to melt thecopper-silver alloy filler rings to securely join components of a heatpipe and fill any gaps between components and comprising an inputbracket assembly being mounted adjacent to the input end of the brazingfurnace and comprising a flat top being parallel to the floor of thesteel liner and having a front edge, two side edges and a rear edgehaving a rectangular notch; two elongated legs being connectedrespectively to the side edges of the flat top and protruding down; anda drive pulley being rotatably mounted between the elongated legs underthe flat top and being aligned with the rectangular notch in the rearedge; an output bracket assembly being mounted adjacent to the outputend of the brazing furnace and comprising a flat top being parallel tothe floor of the steel liner and having a rear edge, two side edges anda front edge having a rectangular notch; two elongated legs beingconnected respectively to the side edges of the flat top and protrudingdown; and an idler being rotatably mounted between the elongated legsunder the flat top and being aligned with the rectangular notch in thefront edge; and a steel mesh belt being mounted around the drive pulleyof the input bracket assembly and the idler of the output bracketassembly in a loop and comprises an upper outbound leg after passingaround the drive pulley sliding along the flat top of the input bracketassembly on which heat pipe assemblies that have not been brazed areplaced on the steel mesh belt, the floor of the steel liner of thebrazing furnace where the components of the heat pipes are brazed andcooled and the flat top of the output bracket assembly where the brazedheat pipes are robotically removed for final fabrication and extendingaround the idler; and a lower return leg extending from the idler,passing under the output bracket assembly, the brazing furnace and theinput bracket assembly and engaging the drive pulley.
 2. The device asclaimed in claim 1, wherein adjacent heating elements of the multi-stagebrazing heater longitudinally overlap somewhat.
 3. The device as claimedin claim 1, wherein the front edge of the input bracket assembly abutsthe input end of the housing.
 4. The device as claimed in claim 1,wherein the drive pulley is driven by a motor mounted under the flattop.
 5. The device as claimed in claim 1, wherein the rear edge of theoutput bracket assembly abuts the output end of the housing.
 6. Thedevice as claimed in claim 4, wherein the drive pulley is driven by ashaft.
 7. The device as claimed in claim 4, wherein the drive pulley isdriven by a gear train.